The present invention relates to a method of and an apparatus for applying sheets of material to a moving surface, and in particular to a high speed tape applicator for applying adhesive tape to a moving web of material.
Devices are known for severing predetermined lengths of tape on machines and applying the lengths of tape to a web of material in continuous motion. One such device is disclosed in the U.S. Pat. No. 2,990,081 to R. P. DeNeui et al., entitled APPLICATION OF TAPE TO MOVING OBJECTS, assigned to the same assignor of the present application. That device comprises a rotatably mounted tape-applying wheel and a vacuum operative within the tape-applying wheel to hold the severed length of tape against the peripheral surface of the tape-applying wheel. The tape is transferred to an article when the article and the wheel bear against each other at a tape-applying station with the tape between them. The device for severing the length of tape includes a device which presses the cutting edge of a knife against a planar surface on the peripheral of the tape-applying wheel to sever the length of tape from a tape feed moving between the knife and the tape-applying wheel. While the severing device is suitable for severing adhesive coated material at relatively low speeds, this device presents certain undesirable adjustment and maintenance problems. First, a high force must be exerted by each cutting edge against the surface of the tape-applying wheel to sever the tape. Second, the machine must be precisely constructed to afford accurate positioning of the knives, and periodic adjustment is required to compensate for wear of the cutting edges and of the tape-applying wheel. Third, it is not suitable for high speed web movement.
In addition to the above-mentioned difficulties, pressure-sensitive adhesive tapes, which have traditionally been applied to moving webs of material, frequently adhere to adjacent layers of tape on the tape supply rollers, making consistent and reliable unwinding difficult. One approach to solving this problem has been to use heat sensitive adhesive tape in lieu of the pressure sensitive adhesive tape, since such tape does not adhere to adjacent layers unless heated.
U.S. Pat. No. 4,909,885 to Swenson, is entitled APPARATUS AND METHOD FOR APPLYING HEAT-SENSITIVE ADHESIVE TAPE TO A WEB MOVING AT HIGH SPEED and is assigned to the same assignor as the present application. This patent discloses an apparatus for applying heat sensitive adhesive tape of the type having a layer of heat sensitive adhesive material that is tacky at an elevated temperature substantially greater than room temperature but not tacky at room temperature to a web of material. However, the high temperatures required to apply the tape can cause the tape, or the web to which the tape is being applied, to become overly softened, thereby losing its integrity and stretching or tearing during application of the tape.
In prior devices, the adhesive tape is held against the tape-applying wheel by a vacuum and then cut directly on the tape-applying wheel. To provide space between the various cut pieces of adhesive tape attached to the vacuum wheel, the devices include a feed roller. During operation, the teed roller is constantly moving in conjunction with the cutting device, thereby spacing the adhesive tape segments along the tape-applying wheel. The vacuum holds the adhesive tape fed to the applying wheel in a sliding arrangement with the circumferential surface of the tape-applying wheel, thereby preventing the adhesive tape from tearing. Without the combination of the feed roller and the vacuum, the segments of adhesive tape could not both be held in radial alignment with the tape-applying wheel and spaced along the tape-applying wheel.
A need exists for a method of and a device for applying adhesive tape to a web of material while the material is moving at high rates of speed, e.g. above 1,000 linear feet per minute.